This invention relates to a grinding method and an apparatus of an orientation flat for a disc-like workpiece such as a silicone wafer, and especially to a grinding method and an apparatus in which disadvantages of a conventional copying master system or a three-axis control NC system are improved, grinding by two-axis control is enabled, and reductions in overall dimension and manufacturing cost of the apparatus are accomplished.
A wafer such as a silicone wafer is a generic name of a thin disc-like semiconductor, in which a disc-like plate is cut away from a cylindrical refined single-substance crystal mother material to be ground to a mirror surface, and various semiconductive elements are formed on the surface by means of an etching process etc. In the silicone wafer, its dimensions are such that a diameter ranges from 10 to 400 mm.phi., a thickness ranges from 200 microns to 10 mm and its shape is formed into a disc-like shape, and an orientation flat (generally abbreviated to OF) is formed by grinding a part of its outer periphery into a straight edge in order to ease its alignment of circumferential orientation.
On the other hand, what causes a trouble in carrying out a fine machining on the wafer surface is dust produced from the surface or outer peripheral surface of the wafer, and more dust will be produced when the outer peripheral surface of the wafer is sharp. Therefore, if a joining surface between the straight edge of orientation flat and the outer peripheral surface is formed into a circular-arc like shape, this will become an effective measure for controlling the dust.
Machining a wafer diameter and the orientation flat to correct dimensions will lead to a reduction in a positioning time of a fine machining in the next process, so that a high-precision grinding is required thereto.
Conventionally, the copying master system has been employed for one method to machine the straight edge of the orientation flat and both sides circular-arc portion of wafer to correct dimensions. In this system, a master having the same shape as a machining standard (completed product) has been made, and a wafer serving as a workpiece has been ground using a mechanical copying mechanism by copying said master. Therefore, it has been required to newly make a master or at least exchange the master every time the completed shape of wafer is changed, so that a manufacturing cost of the master has been costly and much man-hours have been spent for a preparation work.
When the copying master has not been used, it has been necessary to put in use a general NC grinding machine. In this case, it has been required to use a three-axis control system for a rotation direction (.theta.), a longitudinal direction (X-axis) and a lateral direction (Y-axis) of the workpiece. It has been general method to machine the circular-arc portion of orientation flat by means of the three-axis control, and the straight portion by means of the X-axis control only. However, since the three-axis control has been indispensable for this system, the entire apparatus has become complicated, large and expensive.